1. Field of the Invention:
The claimed invention relates generally to surveillance systems, and in particular to an electronic video transmission system for providing continuous surveillance over a predetermined area in which video information is secured in such a manner that it cannot be detected by conventional television receivers.
2. Description of the Prior Art:
The business need for surveillance of business and industrial operations is well established. Visual observation by security personnel is commonly employed for a business as well as security purposes. Surveillance is needed to monitor the presence of unauthorized persons, to monitor the whereabouts of employees entering and leaving, employee performance and efficiency, to determine the existence of fires or other unsafe conditions, to detect theft of equipment or goods through rear doors of an establishment, and to monitor the activities of delivery personnel.
The degrees of security and level of surveillance may vary from building to building or from area to area within a large building. For example, security is required for business operations in which a product is being manufactured according to a proprietary technique which is maintained as a trade secret. In addition, government contractors may from time to time engage in the manufacture of equipment which must be maintained confidential or secret. Certain records maintained by banks and security dealers likewise require a high degree of security. Thus there are a number of operations in which the security of surveillance as well as general security is of paramount importance.
A widely used method for providing continuous surveillance over a predetermined area is by video transmission. The most elemental video surveillance system consists of a single camera permanently connected to a video monitor through a closed circuit transmission line. The transmission of surveillance information through the closed circuit transmission line is relatively secure and immune from unauthorized reception. However, the closed circuit video transmission arrangement cannot be used for certain applications in which it is impossible or not practical to install a closed circuit transmission line. In some instances, it is important to conceal the existence of the surveillance equipment so that surveillance can be performed without the knowledge of personnel within the area. In such situations it is desirable, of course, to miniaturize the equipment used, to conceal it from view, and to make it easy to install and remove so that it can be rapidly removed and set up in different locations from time to time.
A wireless video transmission system satisfies the requirements for area surveillance and miniaturized equipment is available which is easily concealed and which is easy to set up and remove. However, a video transmission signal transmitted over a portion of the frequency spectrum allocated to television broadcasting is subject to interception and monitoring by unauthorized persons through an ordinary television receiver. A conventional method for disguising or concealing the surveillance information which is carried by the video signal is to encode the video data on a line-for-line basis and decode it in a modified video receiver. However, such a complex arrangement requires elaborate data processing equipment for both the transmitter and the receiver, and requires a relatively large amount of power for transmission. Such arrangements are not compatible with battery powered miniaturized equipment in which it may be desirable to operate for an extended period on a limited capacity battery.